1. Field of the Invention
The present invention relates generally to corrosion testing, and more particularly to sulfur-based corrosion testing of electrical components.
2. Background Information
Sulfur is known to cause corrosion in electrical components having silver in the materials used for the components' fabrication and assembly. Because of its low cost and favorable electrical, chemical, and mechanical properties, silver finds many uses in electrical components. For example, silver is used as the base conductive element in thick film resistors or as a component of solder used to attach electrical components to printed circuit boards. Sulfur may be present in many different forms in the environments in which an electrical component may be used. Even relatively small concentrations of sulfur compounds such as hydrogen sulfide (H2S) or sulfur dioxide (SO2) may react with silver to form nonconductive sulfide corrosion products which may cause open circuit failures in electrical components. However, sulfur-based corrosion typically occurs very slowly. An electrical component may perform for years before it fails from sulfur-based corrosion.
Electrical components may be subjected to environmental tests in order to measure failure rates related to sulfur-based corrosion. Unfortunately, because of the relatively slow rate at which sulfur-based corrosion may occur, it may be difficult to obtain statistically significant failure results, even when components are exposed to sulfur compounds for hundreds of hours. So few test failures occur using known test methods that it may be difficult to correlate failure rates based on test results with actual field failures. Also, long duration tests are relatively expensive to perform. Higher temperatures may accelerate sulfur-based corrosion, so the time duration of an environmental test may be reduced by increasing a temperature at which the test is conducted. However, some electrical components may be damaged by exposure to temperatures that are high enough to cause a significant reduction in environmental test time when conventional test methods are used.
Electronic components may be protected from some forms of corrosion by coatings of relatively inert materials. For example, adhesives, potting compounds, and conformal coatings that include silicone polymers in their compositions are known to provide good protection from many different forms of chemical corrosion. However, coatings which include silicone polymers have been known to offer poor protection against sulfur-based corrosion.